Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.60   10.156%   $259.5275   $259.53   $259.55   $259.50  
  Purchase #2 $60.81   7.424%   $65.3245   $65.32   $65.30   $65.30  
  Purchase #3 $157.71   10.120%   $173.6703   $173.67   $173.65   $173.70  
  Purchase #4 $5.59   3.596%   $5.791   $5.79   $5.80   $5.80  
  Purchase #5 $187.61   12.198%   $210.4947   $210.49   $210.50   $210.50  
  Purchase #6 $161.94   8.660%   $175.964   $175.96   $175.95   $176.00  
  Purchase #7 $37.52   13.720%   $42.6677   $42.67   $42.65   $42.70  
  7 purchase totals = $846.78       $933.4397   $933.43   $933.40   $933.50